Permanent magnet stators

ABSTRACT

Annular magnets, primarily for motor stators, are centrifugally cast from particulate materials and synthetic plastic materials. Iron particles and ferrite particles stratified during the spin casting procedures so that the former provide an outer stratum that serves as a yoke in the permanently magnetized structure. The anisotropic ferrite particles are magnetically oriented during casting by a rotating center magnet with the aid of bucking magnets that also rotate and serve to confine the field of the center magnet to the cavity area. Apparatus for carrying out the process is disclosed and includes means for introducing the plastic and particulate materials to the mold cavity while the mold is rotating as well as mold arrangements that facilitate material introduction by the creation of reduced pressure conditions in the cavity during the rotation of the mold. Permanent magnets or electromagnets may be used for ferrite particle orientation and compound magnets made from laminated and facially polarized rubber magnetic sections and which are arcuately bent are disclosed.

BACKGROUND OF THE INVENTION

The invention relates to permanently magnetized annular structuresuseful primarily for stators in dynamo electric machines, and moreparticularly to stators that are molded from synthetic plastic materialswhich serve as a matrix for embedded particles of magneticallyanisotropic ferrite materials that have been magnetically orientedduring the molding of the plastic material. The stator structurescontemplated by the invention are preferably molded by centrifugalcasting procedures, and the invention further relates to methods ofmanufacturing such stators and to certain devices that are useful incarrying out the centrifugal casting procedures.

The use of particulate anisotropic ferrite materials in the manufactureof permanently magnetized structures is well advanced in the art. Suchmaterials have a hexagonal crystal structure and exhibit the phenomenawhen subjected to a highly intense magnetic field of retaining a highermagnetic charge in one direction in the crystal structure than inothers. The anisotropic ferrite materials have the advantage over manyof the metal and metal alloy types of permanent magnets, such as thosemade from alnico, in that they exhibit a higher coercive force and henceare especially suitable for many applications where vibrations and otherdemagnetizing phenomena make it unsuitable to use the cast metalmagnetic structures.

One of the problems which has confronted the industrial use of theanisotropic ferrite materials resides in the attainment of high densityferrite structures that provide a high remanence in the finished magnet.One of the approaches which has been taken to overcome this problem inthe manufacture of permanently magnetized ferrite stators used in motorsand other dynamo electric machines has been to mold the particulateferrite materials under high pressures and to thereafter sinter themolded structures so as to attain the structural stability needed forthe contemplated application. Such procedures usually provide for asuitable magnetic orientation of the particles during the moldingprocedures and the subsequent subjection of the sintered product to anintense magnetizing field along the path of orientation to develop thedesired remanence in the cast structure. The sintering procedures haveseveral disadvantages, among which may be mentioned the fact that theresulting structures are brittle, are frequently warped as a result ofthe sintering process and thereby unsuitable for the intendedapplication, and frequently provide a magnetic field with a nonuniformflux density.

Attempts have also been made to manufacture annular magnetic structuresfrom the anisotropic materials by procedures which avoid the sinteringsteps. Such attempts have involved the casting in an appropriatelyshaped mold of a suitable plastic material containing a suspension ofthe anisotropic ferrite particulate materials. During such procedures,and while the plastic material is fluid or in a semi-fluid state, theferrite particles are magnetically oriented in accord with the desiredpolar arrangement in the stator structure. Such procedures, althoughbeing useful, suffer from the difficulties associated with theattainment of high particle densities and thus the high remanence valuesin the cast stator products. Experience has shown that the highviscosities which are encountered in handling a deformable mass ofsynthetic material containing high concentrations (e.g. greater than80%) of the particulate anisotropic ferrite materials still require highmechanical pressures to be exerted during the casting procedures inorder for the materials to take the shape of the mold or die, and thatthe high viscosities also tend to deter mobility of the particles asthey are magnetically oriented during the casting procedures.

BRIEF SUMMARY OF THE INVENTION

The inventor has found that by using centrifugal casting procedures inthe molding of stator structures from deformable mixtures of hardenableplastic materials and the ferrite particles that the superior remanencevalues associated with the sintered products are attained in thefinished stator structures and, among other things, that deformablemixtures with relatively lower particle densities can be subjected tothe casting procedures to attain the high remanence values in thefinished magnetic products. This may be attributed to the compacting ofthe particulate material in the plastic matrix under the centrifugalforces involved in the casting procedures.

The centrifugal casting procedures involved also lend themselves to theincorporation of fibrous reinforcing material in the cast structure andwhich heretofore by the more conventional molding procedures havedetracted from the attainable particulate loading of the ferritematerial in the castable masses. The procedures further lend themselvesto the attainment of a one piece cast stator structure that has a highdensity peripheral stratum of ferromagnetic particulate material andwhich serves as a yoke in the permanently magnetized stator structures.This stratum surrounds the inner stratum containing the particles ofmagnetically anisotropic material which is oriented to provide the fluxproducing structure for the permanent magnet. The procedures alsofacilitate the attainment of stator structures which cosmetically aremore appealing in certain applications, the procedures making itpossible to provide a thin peripheral stratum of more acceptableappearing nonmagnetic particulate materials.

In accord with certain aspects of the invention, the magneticallyattractable anisotropic ferrite particles are oriented in the plasticmatrix during the centrifugal casting procedure by means of a magnetwhich is centrally located along the spin axis of the mold and which isso shaped and arranged to provide the desired pole faces in the caststructure. In accord with the preferred procedures, the return flux pathfor this magnet is oriented during the casting procedure so as toprovide a high flux concentration which traverses the mold area in whichthe anisotropic ferrite particles are housed. This is accomplished bywhat may be termed as a "bucking" magnetic structural arrangement thatrotates about the spin axis at the perimeter of the mold and in anarrangement such that each pole of the centrally located magneticstructure is facially confronted at the perimeter of the mold by a likemagnetic pole that serves to orient and confine the flux path primarilyto the cavity area of the mold. These particle orienting and buckingmagnets may be permanent magnets or electromagnets as will besubsequently seen.

Various procedures may be employed in centrifugally casting the statorstructures. In accord with certain aspects of the invention a processand apparatus is provided which permits each component of thecentrifugal cast structure to be separately introduced into the cavityof the mold during the casting procedure. This method and apparatus hasthe advantage, as will be subsequently seen, of avoiding the handling ofhighly loaded and viscous mixtures while, nevertheless, permitting theattainment of maximum particulate loading in the desired regions of thestator structure. The centrifugally casting procedures also lendthemselves to the use of liquid synthetic resinous materials which arechemically catalyzeable to form the hardened matrix material as well asto the use of thermoplastic and thermosetting synthetic materials.

A general object of the invention is to provide improved permanentmagnet structures of the annular type that may be used as statorcomponents in dynamo electric machines. Yet another object of theinvention is to provide improved procedures and apparatus for use inmanufacturing annular stator structures from particulate anisotropicferrite materials and hardenable resinous materials and which permit theattainment of the high density concentrations heretofore associated withsintered products. Yet another object is to provide methods andapparatuses for orienting and attaining high concentrations ofanisotropic ferrite particles in plastic structures and without the needfor preparing highly thixotropic mixtures that require high moldingpressures in order to adequately mold such materials. Yet another objectis to provide methods and apparatuses for manufacturing one piecepermanently magnetized stators for dynamo electric machines. A furtherobject of the invention is to provide methods and apparatuses forproducing stator structures that avoid the need for sintering proceduresbut which are nevertheless capable of attaining comparable ferriteparticulate densities in the finished products. Other objects will beapparent from the following description and disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end elevational view of an annular permanently magnetizedstructure embodying certain principles of the invention;

FIG. 2 is a longitudinal section view along the axis of the permanentmagnet seen in FIG. 1 and as taken along the lines 2--2 thereof;

FIG. 3 is a side elevational view with certain parts broken away andothers shown in broken lines of a two pole electric motor utilizing theannular permanent magnets seen in FIGS. 1 and 2;

FIG. 4 is an end elevational view of a one piece annular statorstructure embodying the principles of the invention;

FIG. 5 is a top plan view of the structure seen in FIG. 4;

FIG. 6 is a sectional view along the lines 6--6 of FIG. 4;

FIG. 7 is a side elevational view with certain parts in section andothers broken away or shown in broken lines of a two pole permanentmagnet motor utilizing the stator structure shown in FIGS. 4-6;

FIG. 8 is a side elevational view of a mold and associated apparatusthat may be used in centrifugally casting the stator structuresillustrated in the previously mentioned figures, certain parts beingbroken away;

FIG. 9 is an end elevational view taken along the lines 9--9 of FIG. 8;

FIG. 10 is a transverse sectional view through the mold and its cavityarea as seen along the lines 10--10 therein;

FIG. 11 is a sectional view along the axis of the mold and as seen alongthe lines 11--11 of FIG. 9;

FIG. 12 is a sectional view along the plane common to the axis ofrotation of yet another mold structure and associated apparatus whichmay be used in centrifugally casting the stator structures, the viewalso showing a mechanism for feeding the components of the contemplatedstator to the mold with certain parts being broken away and othersillustrated in broken lines;

FIG. 13 is an end elevational view of the mold as seen along the lines13--13 of FIG. 12;

FIG. 14 is a sectional view taken transverse to the axis of rotation ofthe mold seen in FIG. 12, and as taken along the lines 14--14 therein;

FIG. 15 is a sectional view through yet another embodiment of anapparatus used for centrifugally casting the stator structures and whichis taken along a plane common to the axis of rotation of the moldstructure, certain parts being broken away and others omitted tofacilitate a better understanding of the arrangement;

FIG. 16 is a sectional view through the mold seen in FIG. 15 as takentransverse to the axis of rotation along the lines 16--16 thereof;

FIG. 17 is a side elevational view of a device for magneticallysaturating the stator structure along the path of orientation of theplastic encased anisotropic particles;

FIG. 18 is a vertical sectional view taken along the vertical axis ofthe arrangement seen in FIG. 17; and

FIG. 19 is a transverse horizontal section taken along the lines 19--19of FIG. 18.

DETAILED DESCRIPTION OF INVENTION

The permanent magnets contemplated by the invention have a matrix ofhardened synthetic plastic material which contains dispersed particlesof one or more magnetically anisotropic and magnetically attractableferrite materials which are magnetically oriented in the hardened matrixas the plastic material is caused to harden during the castingprocedure. In a preferred embodiment, the annular permanent magnet hasan annular stratum of particulate, highly permeable ferromagneticmaterial which is located at the outer peripheral surface of the annularmember and surrounds an inner stratum of magnetically orientedanisotropic ferrite particles.

The magnetically attractable ferrite materials which have been founduseful in the practice of the invention have a hexagonal crystalstructure and are magnetically anisotropic in that they have apreferential direction in which they retain a maximum magnetizing forcewhen subjected to a magnetic field. As such, in particulate form, suchmaterials tend to orient themselves so that the preferential directionis aligned with the flux path of the magnetizing field. Such "ferrite"materials are well known in the art and may be exemplified by the bariumferrite, copper ferrites, chromium ferrites, nickel ferrites, cobaltferrites, stronsium ferrites as well as the lead ferrites, magnetites,franklinites, hematites to name but a few. Such materials may be usedalone or in various combinations to tailor the B and H factors. Suchmaterials are known to exhibit magnetic anisotropic properties in singledomain particle sizes, and particles of such materials may be used inparticle sizes ranging from about 3 to 10 microns.

The ferromagnetic materials of high permeability that are useful whenincorporated in particulate form in the stator structures are also wellknown in the art. Such materials are magnetically isotropic and includesoft iron as well as numerous ferroalloys well known in the art.

Apart from the particles of "ferrite" and "ferromagnetic" materials thatmay be used in casting the stator structures, various particulate formsof nonmagnetic materials may be utilized to provide surface colorationsand surface appearances which are more aesthetically acceptable incertain applications for the stators. For example, particulate aluminumand other nonmagnetic metal and metal alloys may be used in particulateform as well as the pigments commonly used as fillers and colorants inplastic and paint formulations, such as Ca Co₃, Ti O₂, lamp black, etc.

Various different types of synthetic plastic materials may be used inthe centrifugal casting procedures advocated herein. The principallimitation on such materials is that they must be sufficiently fluid orcapable of being rendered sufficiently fluid to provide a mass with theincorporated particulate material that is sufficiently deformable underthe centrifugal forces involved to take the form of the mold andsimultaneously permit migration of the particles under the magnetic andcentrifugal forces encountered in the procedures. The inventioncontemplates the use of liquid thermosetting synthetic resinousmaterials which are hardened by the application of heat during thecentrifugal casting procedures, solid commutated thermoplasticssynthetic resinous materials which are rendered sufficiently fluidduring the centrifugal casting procedures by the application of elevatedtemperatures to the materials and thereafter cooled to effectuatehardening, as well as the liquid polymerizable synthetic materials whichare hardened during the centrifugal casting procedures by theincorporation of chemical catalyzing agents that serve to effectuatecompletion of the polymerizations and hence hardening of the liquidmaterials. Among the thermosetting synthetic resinous materials whichmay be employed may be mentioned the urea-formaldehydes, phenolformaldehydes, melamine formaldehydes, as well as the cross linkingpolyesters and alkyds among others.

Among the thermoplastic synthetic resinous materials which may beemployed may be mentioned the chain linked vinyls, acrylics,polyurethanes, cellulose acetates, polyesters, polycarbonates andepoxies among others.

Typical liquid synthetic resinous materials which are commonly hardenedby chemical catalyzing agents are of course the solvent soluble ordispersable monomeric and polymeric materials such as the alkyls,aminos, epoxies, furans, polybutadienes, polyesters among others. Suchmaterials are commonly hardened by the well known peroxide chemicalcatalyzing agents such as alkyl peroxide, the ketone peroxides andothers well known in the art.

Reference is now made to the annular magnetic structure shown in FIGS. 1and 2 and which shows an embodiment of certain principles of theinvention in its simplest form. In this instance the magnet is shown inthe form of a one piece annular member 10 which has an axis 11 ofsymmetry that extends through the hollow 12 of the toroidal member. Thehollow in this instance is adapted for reception of a rotatable memberof a dynamoelectric machine such as a motor armature. Member 10 has acylindrical outer peripheral surface 13 and a cylindrical innerperipheral surface 14. These surfaces 13 and 14 are offset from the axis11 and are radially spaced apart as is evident from FIG. 1.

The centrifugally cast member 10 is composed of dispersed particles 16of a suitable magnetically anisotropic material such as one of thebarium ferrite materials and the particles are embedded in a matrix 17of hardened synthetic plastic material such as a chemically hardenedpolyester resinous material.

As will be subsequently seen, during the centrifugal casting procedurethe magnetically attractable anisotropic particles were subjected toboth magnetic and centrifugal forces. These forces served to concentrateand compact the anisotropic particles into a pair of strata or regions19 of generally arcuate shape and wherein the particles aresubstantially uniformly concentrated in the matrix material. Themagnetic forces were applied between diametrically oppositely locatedand oppositely polarized pole faces located in the hollow 12 during thecasting procedure. This served to magnetically align the particles inthe regions 19 generally along the paths indicated by arrows 20 in FIG.1 and to simultaneously establish arcuate pole faces 21 and 22 ofopposite polarity at diametrically opposite sides of the innerperipheral surface 14 of the annular member 10. These pole faces 21 and22 extend between the opposite ends 23 and 24 of member 10 and due tothe magnetic attraction for the particles which is exerted by theparticle polarizing magnet during the casting procedure, the regions ofsubstantially uniform particle concentration are substantiallycontinuous between the pole faces 21 and 22 in the annular structure butare offset radially from the inner peripheral surface 14 between thecircumferentially spaced pole faces. This results in diametricallyoppositely located arcuate regions 25 in the matrix material and whereinthe particulate concentration of the anisotropic material is less thanthat in the surrounding stratums 19 of substantially uniform particulateconcentration. It is believed that during the centrifugal castingprocedure the particles in the regions 25 tend to move radiallyoutwardly of the axis 11 under the centrifugal forces acting on theparticles and that the resulting compactness in the peripheral stratum19 adjacent these regions 25 causes circumferential particle movementtoward the pole faces 21 and 22 while the matrix material remainsdeformable so that the particles are compacted at the pole faces 21 and22 by a combination of magnetically attracting forces exerted at suchfaces and centrifugal forces which act upon the particles in thecircumferential space therebetween.

The particles retain a certain amount of residual magnetism as aconsequence of the magnetic orientation involved during the hardening ofthe matrix and they may be further magnetized to saturation in asuitable magnetizing fixture which will be subsequently seen.

FIG. 3 illustrates the use of the annular magnet 10 as a component ofthe stator 33 for a two pole DC motor 27. As seen therein, the annularmagnet 10 is housed in the hollow 31 of an annular member 28 made from asuitable highly permeable ferromagnetic material such as soft iron andin a coaxial arrangement which is common to the axis 29 for rotation ofthe armature component 30 of the motor. The annular member 28 in thisinstance serves as a flux transmitting yoke for the annular magnet 10and is so arranged in the assembly that its cylindrical inner peripheralsurface 32 is contiguous with the cylindrical outer peripheral surface13 of the toroidal permanently magnetized component of the stator 33.Motor 27 has a pair of end bells 34 and 35 which are suitably secured atthe opposite ends of the stator 33 structure and which house bearings inwhich the shaft 36 is journaled for rotation about axis 29. Thecommutator and brush assembly (not shown) are of conventional design andare housed adjacent the end 37 of stator 33 in the end bell designatedat 34.

FIGS. 4 through 6 illustrate a one piece annular structure cast bycentrifugal casting procedures advocated herein and wherein the fieldcollapsing yoke is formed from particles of highly permeableferromagnetic material which are embedded in the matrix together withthe anisotropic ferrite particles prior to the hardening of the matrixmaterial. The stator 40 in this instance comprises a matrix 41 ofhardened plastic material which has a thin, generally cylindricalstratum 42 composed of particles 43 of nonmagnetic material such ascalcium carbonate. This stratum 42 is located contiguous to and at thecylindrical outer peripheral surface 44 of the annular component 40.Radially inwardly of this stratum 42 is yet another annular stratum 45of particulate material. This stratum 45 is composed primarily offerromagnetic particles 46 which are embedded in the matrix and whichserve the function of a yoke in the permanently magnetized statorstructure 40. Radially inwardly of the yoke forming stratum 45, theplastic material serves as a matrix in which the ferrite particles 47are embedded. These particles 47 have been subjected to both magneticand centrifugal forces during the casting procedure in a manner similarto those described in the consideration of the magnetic structure shownin FIGS. 1, 2 and 3. Consequently, the structure 40 has generallyarcuate high density regions or strata 48 of substantially uniformparticulate concentration. These regions 48 are contiguous to the yokeforming cylindrical stratum 45 and as in the previous embodiment extendbetween the opposite pole faces 49 and 50 that are formed along thecylindrical inner peripheral surface 51 of the structure during thecasting procedure. Again like the previously described magneticstructure, the structure shown in FIGS. 4, 5 and 6 has arcuate regions52 between the circumferentially spaced pole faces 49 and 50 in whichthe concentration of the ferrite particles is less than that in the highdensity regions 48.

In the formation of the toroidal stator structure 40 by the centrifugalcasting procedure the particles 47 of anisotropic ferrite material aremagnetically oriented by means of a two pole magnet that is located inthe hollow 53 of the stator 40 and rotates about the axis 54 of symmetryfor the structure as the various particles are fixed in the variousregions during the hardening of the matrix material. This aligns thepolar axes of the ferrite particles with the exterior flux path from themagnet as generally indicated by the arrows 55 in FIG. 4. The particlesare thereafter saturated in appropriate magnetizing fixtures to providea permanently magnetized annular stator component 40, as will besubsequently seen.

The stator shown in FIGS. 4, 5 and 6 has the advantage that the yokeforming and magnetized components are all embodied in a one piece moldedstator structure that has an aesthetically appealing surface appearancedue to the peripheral stratum and which can be simply assembled for useas the stator component of a motor such as shown in FIG. 7. In FIG. 7the annular stator 40 is seen as a component of a two pole DC motor 58.The motor 58 has opposite end bells 59 and 60 which are press fit ontothe outer peripheral surface 44 at the opposite ends 61 and 62 of thehollow annular member 40. The armature 63, shown in broken lines, iscoaxially arranged in the hollow 53 of the stator 44 and is mounted onthe drive shaft 64 of the motor. This shaft 64 is journaled at itsopposite ends in suitable bearings 65 and 66 mounted within the endbells in a conventional manner. The commutator and brushes (not shown)are again of conventional design and are mounted internally in end bell59.

Reference is now made to FIGS. 8-11 and wherein a casting apparatus 69for use in centrifugally casting annular magnetic structures is shown asincluding a generally cylindrical, hollow mold 70 that has a toroidal orannular cavity area 71 in which the annular magnets may be centrifugallycast by procedures which will be subsequently described. The mold 70 isconnected by machine screws 72 to the end flange 73 of a driven shaft 74that is coaxially aligned with the axis of rotation for the mold 70 andserves as a means for rotating the mold 70 about its longitudinal axis75.

The mold 70 includes a hollow annular member 76 made from suitableferromagnetic material, such as iron, for reasons which will besubsequently explained. It also includes a pair of circular disk-typeend caps 77 and 78 which are provided with recessed facial surfaces 79and 80 to facilitate a threaded connection with the annular member 76 atits opposite ends 81 and 82. The cylindrical inner wall 83 of member 76defines the outer perimeter of the cavity area 71, and the recessedsurfaces 79 and 80 of the end caps form the perimeters at the oppositeends 84 and 85 of the cavity area. The end caps, in this instance, aremade from aluminum or other suitable metal or alloy having a lowpermeability for reasons which will be subsequently explained.

Along the axis 75 of rotation for the mold 70, the mold is equipped withan elongated solid cylindrical core structure 87. This core 87 issurrounded by the cavity area and has an axis which is common to that ofthe annular member 78. The outer cylindrical surface 86 of the centercore defines the inner cylindrical perimeter of the annular cavity. Thecore structure 87 has a permanently magnetized component 88 which servesto orient the particles of anisotropic material which are incorporatedin the cavity area during the casting procedure. This component 88comprises a pair of compound permanent magnets 89 and 90 that are fixedat diametrically opposite sides of an elongated, coaxially arranged,cylindrical iron core piece 91 in a manner such as to provide a pair ofcircumferentially spaced arcuate pole faces 92 and 93 for the magneticcore component 88.

The compound magnets 89 and 90 in the illustrated embodiment arecircumferentially spaced apart in the core component. Each compoundmagnet is made up of a plurality of elongated, thin, flat, faciallypolarized, flexible magnetic sections 95 that are flexed to an arcuatecontour in the laminated structure and suitably secured together inface-to-face confronting arrangement where the poles of each section arearranged in a pole complementing arrangement that is apparent from FIG.11. This provides the opposite pole faces 92 and 93 at the diametricallyopposite sides of the cylindrical core structure. As seen in FIG. 10,the compound magnets 90 and 89 and the iron core piece 91 are encased attheir opposite sides between hardened plastic material 96 that may besuitably reinforced for example with glass fibrous material.

The arcuate width dimension of each magnet section 95 in the laminatedarrangement for each compound magnet progressively diminishes radiallyinwardly from the outer cylindrical surface 86 of the cylindrical corecomponent 87. The iron core piece 91 serves to magnetically couple thecompound magnets 89 and 90 and the diminishing section width arrangementin each compound magnet serves to suppress short circuiting flux pathsto the laminates of the structure and facilitates the establishment ofan overall flux path external of the center core 87 which is through thecavity area and generally indicated by arrows 97.

The external flux path for the magnetized component 88 of core 87 isgenerally confined to the cavity area by a pair of thin, flat, flexibleand facially polarized bucking magnets 98 and 99. These magnets aresuitably secured to the outer periphery 100 of the annular mold member76 and are radially outwardly offset from the pole faces 92 and 93 ofthe center core 87. The arrangement of the compound magnets 89 and 90 inthe center core provide magnetic poles of opposite polarity at faces 92and 93 as seen in FIG. 10. Each of the "bucking" magnets 98 and 99 isarranged so that its axially facing polarized facial surface 101 faces apole face of like polarity in the core structure. This provides aninduced like polarized face at the inner wall of the annular member 76such as indicated at 102 and 103 and which serve to confine the fluxfield from the core component 88 generally to the cavity area. The endcaps 77 and 78 in this respect, are made of low permeable material toprevent short circuiting flux paths, as will be well evident to thoseskilled in the art.

The end caps 77 and 78 are provided with aligned cylindrical recesses105 and 106 and the opposite ends 107 and 108 of the center corestructure fit in these recesses in the assembled mold. In this respect,the center core 87 is fixed to cap 78 by means of a pair of aluminummachine screws 109 that threadingly engage the core end 108 at theopposite sides of the compound magnets. The other end 107 of the centercore 87 snuggly fits in the recess in cap 77 so as to facilitate readyassembly and disassembly of the mold structure and the incorporation ofthe moldable materials and removable of the cast product from this endof the mold.

In the process of preparing an annular magnet from particulate ferritematerial in accord with the invention, it is preferable to initiallymagnetically sensitize the "ferrite" particles in a suitable magneticfield. This is done so that each particle of the ferrite materialdevelops opposite magnetic poles and hence is responsive to theorienting magnetic field during the centrifugal casting procedure. Inthis respect, the ferrite particles to be used in the casting procedureare preferably stirred prior to wetting with the matrix forming materialin a suitable magnetic field and for such a period of time as isnecessary to magnetically sensitize substantially all of the particles.This "presensitizing" may be accomplished by simply stirring theparticles in the presence of the matrix forming material and during theformation of the initial mixture which is to be introduced to the mold.However, experience has shown that this "presensitizing" procedure ismore rapidly and effectively accomplished when the particles are stirredin the magnetic field while still in a dry or unwetted state.

The apparatus shown in FIGS. 8-11 may be used for casting either of theannular magnetic structures seen in FIGS. 1-7 and through the use of amatrix forming liquid polymerizable synthetic material which ispolymerized and hardened during rotation of the mold 70 by admixturewith a chemical catalyzing agent.

In carrying out a centrifugal casting procedure using the apparatusshown in FIGS. 8-11, a deformable mass which constitutes a basic mixtureof the materials is initially prepared for introduction to andconfinement in the cavity area 71 of the mold. The basic mix maycomprise an intimate mixture of the magnetically sensitized ferriteparticles and the liquid polymerizable synthetic material together witha suitable catalyzing agent for effectuating the polymerization of thesynthetic material to a hardened state during the centrifugingprocedure. In general, the ferrite particles constitute at least seventypercent by weight of the basic mixture, and this mixture may be formedby simply stirring the solid ferrite particles with the polymerizablematerial and catalyzing agent to provide a suitable dispersion of thesolid particles in the liquid materials involved. In the preferredstator arrangement, an integrally cast yoke forming stratum in themolded structure is desired. In such cases, the ferromagnetic particleswhich are used to form this stratum may be also mixed together with aferrite particulate material and other components during the initialpreparation of the basic mix. The amount of ferromagnetic material usedin forming the basic mixture may vary depending upon the intensity ofthe external field which is to be collapsed by the yoke forming portionof the molded stator, as those skilled in the art will be aware. Ingeneral, the presence of the ferromagnetic particulate material in thebasic mix in a weight ratio of about one part ferromagnetic material toabout five parts anisotropic ferrite material has been foundsatisfactory. However, lesser or greater amounts of the ferromagneticmaterial may, of course, be employed.

Following the preparation of the basic mixture, and prior to anyappreciable polymerization that would interfere with the mobility of theparticles under the contemplated conditions for centrifugally castingthe structure, an amount of the basic mixture sufficient to fill thecavity area of the mold is introduced to the mold by removing andthereafter replacing the end caps 77. As soon as this has been done, themold is then rotatably driven about its longitudinal axis 75. Experiencehas shown that when the basic mixture contains dispersed particles ofboth ferromagnetic and anisotropic ferrite materials in an intimatemixture that the best stratification is accomplished by progressivelyincreasing the rotational speed to a maximum rpm. This maximumrevolutions per minute may be determined empirically as being one whichis just less than that at which the ferrite particles in front of thepole faces 92 and 93 of the center core 87 move radially outwardly fromthe pole faces for reasons of centrifugal forces which exceed themagnetic attracting forces exerted on the particles at the pole faces.

Throughout the centrifugal casting procedure, the ferrite particles aresubjected to the rotating and particle orienting magnetic field producedby the coaction of the core magnet 88 and the blocking magnets 98 and99. This field serves to magnetically align the ferrite particlesgenerally in accord with the flux path indicated by arrows 97. One mayalso stimulate movement of the particles prior to the hardening of thematrix material by subjecting the rotating mold to mechanical vibrationsor by agitating the particles during the casting procedures through theuse of ultrasonic means (not shown). Needless to say, rotation of themold is maintained until such time as the matrix forming materialhardens sufficiently to maintain its structural stability contemplatedby the process. Through use of the centrifugal casting procedure,effectively high density regions of particulate ferrite material may beobtained and which are comparable to those obtained in sintered magnetsmade from such materials.

Reference is now made to FIGS. 12-14 and wherein another apparatus 111for use in centrifugally casting the annular magnetic structures isshown. In this instance the apparatus 111 includes a generallycylindrical mold 112 which is fastened by means of machine screws 113 tothe end flange 114 of a driven shaft 115. This shaft serves as a meansfor rotating the mold about its longitudinal axis 116 as in the previousembodiment. The apparatus also includes a feed mechanism 117 which, inthis instance, is used for delivering the materials that enter into themakeup of the cast component to the annular cavity 118 area of the moldduring the casting procedure. The apparatus 111 is further equipped withradiant heaters 119. These heaters 119 permit the use of thermoplasticpolymeric materials or alternatively thermosetting polymeric materialsfor forming the matrix of the particle laden magnets casted in the mold.

The mold 112 includes a hollow, annular member 120 which is opened atits opposite ends 121 and 122 but which are closed in the assembled moldarrangement by a pair of circular disk-type end caps 123 and 124. Thesecaps have recessed inner facial surfaces 125 and 126, as seen in FIG.12, and are threadingly secured to the annular shell member 120 at itsopposite ends. Like the previously described molding apparatus, theannular member 120 is made of ferromagnetic material, such as iron, andthe end caps are made of aluminum or some other material of low magneticpermeability. The inner cylindrical surface 128 of member 120 definesthe outer perimeter of the cavity area 118 while the recessed surfaces125 and 126 define the opposite ends of the cavity.

The center core component 130 is similar to that described in theprevious embodiment, except that the center pole piece 131 in thisinstance is tubular so as to form a receiving chamber 132 for thematerials that are to be dispensed to the cavity area 118 during thecasting procedure. The core component 130 also differs in that it has aplurality of radially extending and axially spaced apart passageways 133which interconnect the cavity area 118 and the chamber 132 through thehardened plastic area at the sides of the compound magnets 135 and 136.

The recessed surfaces 125 and 126 in the end caps 123 and 124 areprovided with axially aligned recesses 137 and 138 to accommodate theopposite ends 139 and 140 of the cylindrical core component in a mannersimilar to that previously described. Thus the magnetic core is securedto cap 124 by means of metal-type screw fasteners 141 while at the otherend the center core snuggly fits in the center recess 137. Cap 123 hasan annular inner recess 142 which confronts the adjacent end 139 of thecore component 130 of the mold. This recess 142 is coaxially arrangedwith respect to the longitudinal axis 116 of the assembled mold. The cap123 also has a plurality of radially extending passageways 143 whichcommunicate with the annular recess 142. As best seen in FIGS. 12 and13, this end 139 of the core component 130 is provided with a pair ofpassageways 144 that in the assembled mold interconnect the annularrecess 142 and the cavity area 118 at the cavity confronting outercylindrical surface 145 of the cylindrical core component 130. Thisarrangement, as will be subsequently seen, provides a means forexpelling air from the cavity area 118 during the introduction of thematerial to the mold and also has a means for conducting excess materialout of the cavity area 118.

End cap 123 has a bore 146 which communicates with the chamber 132formed by the tubular core piece 131. This bore 146 is axially alignedwith the axis of rotation of the mold. In the embodiment illustrated, anelongated tubular conduit 148 that rotates with the mold is threaded atone end 149 in the bore and is journaled at its opposite end 150 in abushing 151. This bushing is fixed to a block 152 by metal fasteners153. Block 152 has a bore 154 which is axially aligned with the axis ofrotation of the mold and in which the bushing is mounted as seen in FIG.12. This block 152 also has a vertically extending bore 155 whichcommunicates with bore 154 and in which it receives the threaded end ofa conduit 156 of the feed mechanism 117. At its opposite end, thisconduit 156 is connected to the discharge opening of a hopper 157 forreceiving the materials that are fed to the mold cavity by way of thetube component 148 of the feed mechanism 117.

The permanently magnetized component 160 of the center core 130 isprovided by the compound magnets 135 and 136. These magnets are soarranged as to provide diametrically oppositely facing arcuate polefaces 161 and 162 and which are of opposite polarity as in thepreviously described embodiment. Each compound magnet is composed ofthin, flat, resilient, flexible magnetic sections 164 which are arrangedin a face-to-face relation and in a complementing pole arrangement so asto provide an external flux path in the cavity area which is generallyindicated by the arrows 163. The flexible sections 164 again havearcuate width dimensions in the laminated compound magnetic structureswhich progressively diminish radially inwardly from the peripheralsurface 165 of the core 130.

The flux path 163 of the magnetic component 160 is also oriented bymeans of a pair of thin, flat, flexible bucking magnets 166 and 167 thatare facially polarized and secured at the outer cylindrical surface 168of the mold component 120. These magnets, are arranged with respect tothe pole faces of the center core in a manner like that described in theprevious embodiment so that the surfaces 169 and 170 of the annularmember 120 which confronts the arcuate pole faces 161 and 162 across thecavity area have an induced polarity like that of the confronted poleface.

The embodiment shown in FIGS. 12-14 may be used for casting a statorhaving a matrix formed from either solid thermoplastic or liquidthermosetting polymeric material and the following procedures may beemployed in the preparation of a cosmetically attractive and fibrousreinforced stator component.

In utilizing the apparatus depicted in FIGS. 12-14 for forming a statorhaving a matrix of hardened thermoplastic material, the mold 112 isinitially driven at a suitable angular velocity and the components thatgo into the formation of the stator are separately delivered to thecavity area by way of the feed mechanism 117. In a typical process,rotation of the mold 112 about the axis 116 will create a reducedpressure condition in the cavity area. As the mold rotates undercircumstances where the cavity is empty, air in passageways 143 isdisplaced radially due to the centrifugal action transpiring and thiscreates a reduced pressure condition in the annular recess 142 andbecause of the orifice connection 144 with the cavity area also createsa reduced pressure condition in the cavity 118. As a result, there is acontinuous flow of air from the hopper 157 through conduits 156 and 148to the receiving chamber 132 and thence through passageways 133 to thecavity 118. Accordingly, when material is placed in the hopper 157 it issucked into the cavity area 118 for reasons of the existing reducedpressure conditions. In a typical procedure, a predetermined amount ofcommutated, pulverulent solid thermoplastic polymeric material may beadded to the hopper 157. For reasons of the reduced pressure conditionsin the cavity area, this added material will be drawn through conduits156 and 148 into the receiving chamber 132 and from this chamber 132 thematerial will be drawn through passageways 183 into the cavity area 118.Some of the pulverulent material may become entrained and drawn viapassageway 148 into annular recess 142 and from whence it will becentrifugally delivered to the exterior of the mold area throughpassageways 143. However, most of the solid particles will orientthemselves under the centrifugal action transpiring in the cavity arearadially outwardly from the outlet passage 144 toward the inner surface128 of the annular mold member 120. Here by the transmission of heatfrom the radiant heaters 119 the material is heated to the point atwhich it becomes fluid and deformable. When this happens a suitablepulverulent nonmagnetic material may be added to the hopper in order toform an annular stratum in the finished product which provides thedesired external appearance. This material, such as calcium carbonate,may be added alone to the hopper 157 or together with suitably shortlengths of fibrous reinforcement such as glass fibers and will be drawnby the reduced pressure conditions into the cavity area and where itwill become entrained in the fluid plastic material and by centrifugalforce, caused to migrate toward the cylindrical surface 128 of member120. To provide an annular stratum of yoke forming material contiguousto the pigmented calcium carbonate bearing stratum, a predeterminedamount of particulate ferromagnetic material may now be added to thehopper 157 and from whence the particles are drawn by the reducedpressure conditions through conduits 156 and 148 into the receivingchamber 132. From here the particles pass via passageways 133 to thecavity area. These particles then become entrained in the deformablemass of synthetic plastic material and under the centrifugal actiontranspiring migrate radially to compact into a cylindrical stratumcontiguous to that containing the calcium carbonate. The amount of time,of course, which will be required for the materials to migrate to theirproper regions and form a compact mass can be determined in eachinstance empirically by trial and error procedures, and the time, ofcourse, will vary in accord with the density of the particulate materialand centrifugal forces which are involved. Following the addition of theferromagnetic particles to the hopper and after sufficient time has beenallotted to permit the particles to compact into the desired region, apredetermined amount of the sensitized particulate magneticallyanisotropic material may be added to the hopper 157 and from whence itwill be delivered to the cavity area 118. Here the particles will besimultaneously oriented in the deformable plastic material by thecentrifugal action transpiring and by the flux field from the coremagnet. The amount of polymeric material initially added is preferablyslightly in excess of the volume which will be occupied by the matrixmaterial in the cast stator. Accordingly, one can readily determine byexamination of the discharge from passageways 143 when sufficientparticles of anisotropic material have been added to form a compactedmass providing the desired regions adjacent the magnetic core componentof the mold.

When the particulate material has been all added to the cavity area,heating of the mold may be discontinued so that the thermoplasticmaterial hardens as the mold contents cool to ambient temperatures. Therotation of the mold, of course, is continued until the matrix hardenssufficiently to maintain the orientation and particle compactness in thevarious stratum and regions. Thereafter the cast stator may be removedfrom the mold and the anisotropic material may be further magnetized tomagnetically saturate the particles to a suitable remanence value.

When the particulate materials used in forming the various regions orstrata have different densities that permit their separation bycentrifugal action, the materials may be mixed together andsimultaneously added to the hopper for passage to the cavity area.However, the preferred practice is to add each type of particulatematerial separately with the material contemplated for formation of theoutermost stratum being added first and the anisotropic material lastsince this practice avoids appreciable comingling of particles in theadjacent stratum.

Reference is now made of FIGS. 15 and 16 and wherein yet anotherapparatus 171 which may be used for centrifugally casting the statorstructures is illustrated as including a mold 172. The mold is rotatableabout its longitudinal axis 173 and is connected by metal fasteners 174to the end flange 175 of a driven shaft 176. Shaft 176 serves as a meansfor rotating the mold about its axis. The apparatus 171 includes a feedmechanism 177 like that illustrated in FIG. 12, of which only thedelivery conduit 178 is shown in the drawings.

The mold 172 is formed by an annular member 179 that defines thecircumferential outer perimeter of the cavity area 180. The member 179is also equipped at its opposite ends 181 and 182 with a pair ofdisk-type circular end caps 183 and 184. These caps, like the previousembodiment, have inner facial recesses 185 and 186 and are secured tothe shell by means of an internal threaded connection evident from thedrawings.

The elongated, axially arranged core component 187 in this instance hasan electromagnet 188 as opposed to the permanent type magnetic corestructure seen in the previous embodiments. The core magnet 188 has anelongated core piece 189, made of soft iron, and which, as seen in FIG.16 in cross section, has an axially extending bore 190 which is coaxialwith the axis of rotation for the mold structure and serves as thereceiving chamber 191 for the materials fed to the mold 172 from thefeed mechanism. This core piece for the magnet also has radiallyextending passageways 192 which in this instance interconnect the cavityarea in the chamber through the arcuate pole faces 193 and 194established by the core piece. As also seen in FIG. 16, the thickness ofthe core piece, in cross section, progressively increases radiallyoutwardly from the bore 190 forming the receiving chamber and thewindings 195 of the electromagnet are encased in hardened plasticmaterial to provide a continuous cylindrical surface 196 at the innerperiphery of the cavity area 180. Cap 184 has a center recess 197 andhere the electromagnet is secured to the cap by metal screw fasteners198. Cap 184 also has a bore 199 which communicates with the exterior ofthe cap and with a recess 197 which the end of the core is received.Bore 199 accommodates the leads for the core magnet and which areelectrically connected to a pair of slip rings (not shown) but which arefixed to the shaft 176 and electrically connected by suitable brushes(not shown) to a DC power source. The annular member 179 in thisinstance, is also equipped with a pair of electromagnets designated at200 and 201. These electromagnets are connected in series and have apair of leads 202 which are electrically connected to another pair ofslip rings (not shown) that are fixed to the shaft 176 and via suitablebrushes (not shown) to a DC source.

The other end of the core magnet 188 fits in a suitable circular recess205 in the end cap 183. This recess 205 is coaxial with recess 197 andhas an annular recess 206 which is connected with the cavity area bymeans of peripheral end slots 207 in the pole faces 193 and 194 at thisend of the core component of the mold. The annular recess 206communicates with the exterior of the mold by means of radiallyextending passageways 208 similar to the arrangement shown in thepreviously described embodiments.

The apparatus shown in FIGS. 15 and 16 may be used for casting a statorhaving a matrix of either thermoplastic or thermosetting material and toprovide the heating function the apparatus includes a pair of inductionheaters 210 that are radially offset from the mold and rotatablestructure.

In utilizing the apparatus shown in FIGS. 15 and 16, the mold 172 isassembled and initially subjected to rotation about its axis 173 ofrevolution at a suitable angular velocity. This causes a vacuumcondition to be created in the cavity area 180 as previously described.Thereafter a predetermined amount of liquid thermosetting syntheticresinous material is introduced to the cavity area 180 via the feedmechanism 172 that communicates through the end cap bore with thereceiving chamber 191. The fluid material, of course, passes viapassageways 192 to the cavity area from the receiving chamber. Theamount of liquid resinous material added in this instance is preferablyslightly in excess of the requirement for the matrix material of thestator structure so that again complete fullness of the cavity area canbe detected by the expulsion of the excess contents through the radiallyextending passageways in end cap 183. Following introduction of theliquid resinous material, particulate ferromagnetic material may beintroduced to the cavity area to form a peripheral stratum in the fluidresinous material previously incorporated therein. After the yokeforming ferromagnetic particles have suitably migrated and compacted atthe outer perimeter of the cavity area, particulate anisotropic andpresensitized ferrite material may be added via the feed mechanism andin amounts sufficient to displace the excess resin through the slots207. The ferrite material under such circumstances will form an innerstratum in the fluid plastic material in the cavity area and at thispoint, the core magnet 188 can be energized to establish a particleorienting field for the sensitized ferrite material and which isgenerally represented by the arrows 212. Simultaneously, theelectromagnetic "bucking" magnets 200 and 201 can be energized tofurther orient the external path of the flux field of the core magnet.As seen in FIG. 16, the energizing of the electromagnets 200 and 201will provide induced polarities at the diametrically opposite innerfaces 214 and 215 of the annular member and which are like those of theconfronting pole faces 193 and 194 respectively. After the anisotropicmaterial has become suitably compacted and magnetically orientedinduction heaters 210 may be energized to elevate the temperature withinthe mold and accordingly, effectuate hardening of the thermosettingmaterial therein.

Reference is now made to the magnetizer illustrated in FIGS. 17-19 andwherein the magnetizer 220 is seen as associated with a stator 221during the process of magnetically saturating the ferrite particlesthereof.

The magnetizer comprises a first electromagnet with a pair of elongatedshoes 223 and 224 which extend during use of the magnetizer into thehollow 225 of the annular stator component 221. The stator 221 undersuch circumstances is oriented with respect to the pole faces 226 and227 of the shoes so that they face the pole faces 228 and 229 of thestator having opposite polarities.

The magnetizer also includes a second electromagnet 230 which has a pairof elongated shoes 231 and 232 that also extend into the hollow 225. Theshoes 223 and 224 of the electromagnet 222 are spaced apart atdiametrically opposite sides of the hollow as seen in FIG. 19 and theshoes 232 and 231 of magnetizer 230 are located in the space between theshoes 223 and 224. Magnetizer 230 serves as a bucking magnet and shoes231 and 232 are polarized during use so that their polarities are likethose of the adjacent shoes 223 and 224 of electromagnet 222. As such,electromagnet 230 serves to resist a flux path between shoes 223 and 224across the air gap through the hollow and causes the path to traversethat generally represented by the arrows 2 along the path of orientationof the ferrite particles. In the preferred practice, electromagnet 220has a greater number of ampere turns than electromagnet 230. FIGS. 17-19are merely illustrative of the magnetizer arrangement and provision maybe made for withdrawing the shoes from the hollow as in the directionsof arrows 235 to facilitate removal of the saturated stator from themagnetizer.

While only certain preferred embodiments of this invention have beenshown and described by way of illustration, many modifications willoccur to those skilled in the art and it is, therefore, desired that itbe understood that it is intended herein to cover all such modificationsas fall within the true spirit and scope of this invention.

What is claimed as new and what it is desired to secure by LettersPatent of the United States is:
 1. A stator for a dynamoelectric machinecomprising a one piece annular member having an axis and a hollowextending along the axis for the reception of a rotatable member of themachine, said annular member having inner and outer peripheral surfaceswhich are radially offset from said axis and radially spaced apart, saidannular member comprising magnetically anisotropic particles ofmagnetically attractable ferrite material which are embedded in a matrixof hardened synthetic plastic material, said particles beingmagnetically aligned and permanently magnetized along a return flux paththat extends in the member between arcuate pole faces which are ofopposite polarity and circumferentially spaced apart at the innerperipheral surface of the annular member, said annular member having anarcuate region of substantially uniform concentration of said particlesin the matrix material and which extends along the flux path and iscontinuous between said pole faces, said region being located radiallyoutwardly of the inner peripheral surface in the arcuate space betweensaid pole faces, and said member having another region in the arcuatespace between said pole faces and which is located between said arcuateregion and the inner peripheral surface, such other region having aconcentration of said particles which is less than the concentrationthereof in said arcuate region.
 2. A stator in accord with claim 1 whichfurther comprises an annular member of ferromagnetic material having anaxis which is arranged in coaxial relation to the axis of the one pieceannular member, such annular member of ferromagnetic material having aninner peripheral surface which is contiguous with the outer peripheralsurface of the one piece annular member.
 3. A stator in accord withclaim 1 where said matrix of the one piece annular member has an annularstratum of ferromagnetic particles embedded therein, said stratum beinglocated contiguous to and radially outwardly of said arcuate region ofuniform particulate concentration.
 4. A stator in accord with claim 3where said matrix of the one piece annular member has an annular stratumof nonmagnetic particles embedded therein, said stratum of nonmagneticparticles being located at said outer peripheral surface.
 5. A statorfor a dynamoelectric machine comprising a one piece annular memberhaving an axis and a hollow extending along the axis for the receptionof a rotatable member of the machine, said annular member having innerand outer peripheral surfaces which are radially spaced apart, saidmember comprising particulate materials which are embedded in a matrixof hardened synthetic plastic material and which include particles offerromagnetic material and magnetically anisotropic particles ofmagnetically attractable material, said ferromagnetic particles beingarranged in an annular stratum thereof, said magnetically anisotropicparticles being magnetically aligned and permanently magnetized along areturn flux path that extends in the member between arcuate pole faceswhich are of opposite polarity and circumferentially spaced apart at theinner peripheral surface of the annular member, said member having anarcuate region of substantially uniform concentration of saidanisotropic particles and which extends along the flux path and iscontinuous between said pole faces, said annular stratum being locatedradially outwardly of and contiguous to said arcuate region ofmagnetically anisotropic particles, said arcuate region being locatedradially outwardly of the inner peripheral surface in the arcuate spacebetween said pole faces, and said member having another region in thearcuate space between said pole faces and which is located between saidarcuate region and the inner peripheral surface, such other regionhaving a concentration of said anisotropic particles which is less thanthe concentration thereof in said arcuate region.
 6. A stator in accordwith claim 5 where the regions containing anisotropic particles wereformed by centrifugal casting procedures and where the anisotropicparticles were magnetically oriented while rotating about said axis.